1. Field of the Invention
The present invention relates to the field of DC driven electromagnetic actuators and drive circuits therefor.
2. Prior Art
DC driven electromagnetic actuators of various types are well known in the prior art, both in linear and angular actuator form. In many DC powered actuators, the moving member of the actuator remains in the actuated position so long as the power to the actuator is maintained, with a return spring returning the moving member of the actuator to the unactuated position on removal of power from the actuator.
DC powered electromagnetic actuators of the latching type are also well known in the prior art. In such actuators, power is applied to electromagnetically attract the moving member of the actuator to the actuated position, after which power may be removed. The moving member remains in the actuated position by the residual magnetic field due to the retentivity of the material or materials in the actuator. In some cases, the residual magnetic field is provided by a permanent magnet somewhere in the magnetic circuit, or by the inherent retentivity of the material or materials making up the magnetic field which would not normally be considered permanent magnets per se. In the latter case, latching may be provided by low retentivity materials by having a substantially zero air gap magnetic circuit when the electromagnetic actuator is in the actuated condition.
In some applications, DC electromagnetic actuators of the latching type have operated against return springs, with the latched actuator being unlatched by a controlled pulse of limited opposite magnetization polarity from the original latching pulse to demagnetize the magnetic circuit. Such latching actuators have the advantage of latching and unlatching on appropriate current pulses and to remain in either the latched or the unlatched condition for any desired length of time without further dissipation of power. Latching actuators of this kind are described, by way of example, in U.S. Pat. No. 3,683,239, 4,107,546, 4,409,638 and 4,811,221, to name a few.
DC latching electromagnetic actuators of the foregoing kind have also been used in opposing pairs, the second latching actuator replacing the return spring so that the common moving member or moving assembly for the two actuators effectively latches in either of two positions. Though demagnetizing the magnetic circuit of one actuator while magnetizing the magnetic circuit of the other actuator could be done to effect actuation in either direction, normally the opposing actuators are each provided with sufficient pulling force to overcome the force caused by the retentivity of the magnetic circuit of the other actuator, making use of demagnetizing pulses unnecessary. Actuators of this general type are disclosed in U.S. Pat. Nos. 3,743,898, 5,460,329, 5,598,871, and 5,640,987, to name a few. The foregoing latching electromagnetic actuators have the advantage of only requiring short bursts of power when the same change state, and accordingly, as in some of the prior U.S. patents herein before referred to, are suitable for use in battery powered systems such as battery powered sprinkler systems which operate pilot-valve controlling latching actuators a few times a day or less.
Whether used in a battery operated system or not, such actuators normally require a short current pulse of substantial current for proper operation. This usually is provided by charging a capacitor of substantial size and coupling the capacitor across the actuator coil to provide the current pulse, partially or completely discharging the capacitor in the process. In battery operated systems where battery power is very limited, the current obtained in the pulse can exceed the current the battery is capable of safely providing. Even when excess power is available, capacitors are often used adjacent the actuator to avoid resistive voltage drops and noise from the switching of substantial currents through long lines. Such capacitors, however, have the disadvantage of a shorter life and lower reliability than other components of a typical system.
In some applications, speed of operation of the actuator is of prime importance. By way of example, U.S. Pat. No. 5,460,329 discloses a high speed fuel injector which uses a double solenoid spool valve to control the flow of a working fluid that is used to move an intensifier piston of an intensifier type fuel injector, typically used for diesel engine fuel injectors. As shown in that patent, an ideal diesel engine fuel injector will provide a small pre-injection (also referred to herein as a pilot injection), followed by a short delay, followed by the main injection (the graph of FIG. 3 of the foregoing patent has the abscissa inadvertently labeled in seconds instead of milliseconds). The purpose of the pilot injection is to initiate combustion, by way of a small injection, before the main injection is initiated, so that main injection combustion may start at the beginning of main injection and proceed uniformly throughout the main injection period. Without the pilot injection, there is a similar delay after the initiation of main injection before combustion begins, resulting in the characteristic diesel engine knock and energy conversion inefficiencies.
As may be seen from FIG. 3 of the foregoing patent, the ideal pilot injection lasts for a fraction of a millisecond, with a delay between the end of pilot injection and the beginning of main injection being another fraction of a millisecond in a typical diesel engine application. Also as described in the patent, ideally the full main injection flow rate is instantly established at the beginning of main injection and instantly terminated at the end of main injection. In reality, however, prior art fuel injectors have taken considerable time to reach maximum injection rate on initiation of the main injection, and similarly have been slow to terminate main injection. This varying injection rate provides further inefficiencies because much of the main injection is with non-optimum fuel droplet size, resulting in incomplete combustion and a heavy black exhaust.
Thus it may be seen that in applications such as the diesel fuel injector just described, the speed of operation of the actuator is of particular importance.
A method of rapidly energizing an electromagnetic actuator having at least one energizing coil to move a movable member, comprises establishing a current in an inductor through a first circuit; coupling the inductor in series with the coil in a second circuit; and, interrupting the first circuit and directing the current in the inductor of the first circuit to flow through the coil in the second circuit. A method of rapidly energizing a solenoid coil to move a movable member of a solenoid valve for a controlled fuel injector comprises establishing a current in an inductor through a first circuit; coupling the inductor in series with the solenoid coil in a second circuit; and, interrupting the first circuit and directing the current in the inductor of the first circuit to flow through the solenoid coil in the second circuit. A method of rapidly energizing an electromagnetic actuator having at least one energizing coil having first and second coil leads comprises providing an inductor having first and second inductor leads; coupling the first coil lead and the first inductor lead to a first power supply terminal; coupling the second inductor lead through a first diode to the first coil lead and through a first switch to a second power supply terminal; coupling the second coil lead through a second switch to the second power supply terminal; turning on the first switch to establish a current in the inductor; turning on the second switch to couple the inductor in series with the coil; and, turning off the first switch to direct the current in the inductor into the coil. A controller circuit for electromagnetic actuators having at least one energizing coil with first and second coil leads comprises first and second switches; an inductor having first and second inductor leads, the first inductor lead being coupled to a first power supply terminal, the first and second inductor leads being coupled to the first coil lead through first and second diodes, respectively; the first switch controllably coupling the second inductor lead to a second power supply terminal; the second switch controllably coupling the second coil lead to the second power supply terminal, and, a third switch and a third diode coupled in series together and in parallel with the inductor between the first and second inductor leads.